Magnetic recording medium and magnetic storage apparatus

ABSTRACT

A magnetic recording medium includes a nonmagnetic substrate, a soft magnetic underlayer, an orientation control layer, a perpendicular magnetic layer, and a protection layer that are arranged in this order. The perpendicular magnetic layer includes a first magnetic layer and a second magnetic layer that are arranged in this order on the orientation control layer. The first magnetic layer has a granular structure including an oxide at grain boundary parts of magnetic grains, and the second magnetic layer is closest to the protection layer among layers within the perpendicular magnetic layer, and includes magnetic grains made of a CoCrPt alloy, and a nitride of carbon or a hydride of carbon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. patent applicationSer. No. 16/279,143 filed on Feb. 19, 2019, which is based upon andclaims priority to Japanese Patent Application No. 2018-055741 filed onMar. 23, 2018, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic recording medium, and amagnetic storage apparatus including the magnetic recording medium.

2. Description of the Related Art

Recently, the recording density of a magnetic recording medium that isused in a HDD (Hard Disk Drive) has increased considerably. Hence, thestorage capacity of the HDD that is one type of magnetic storageapparatus, has increased accordingly, and it is believed that thistendency for the recording density and the storage capacity to increasewill continue into the future. For this reason, there is active researchto develop a magnetic recording medium having a high recording density,and a magnetic head that records information on and reproduces theinformation from the magnetic recording medium having the high recordingdensity.

The magnetic recording medium used in the magnetic storage apparatusthat is presently commercially available is a perpendicular magneticrecording medium. The perpendicular magnetic recording medium includes aperpendicular magnetic layer having an axis of easy magnetizationprimarily oriented perpendicularly to a surface of a nonmagneticsubstrate. The perpendicular magnetic layer has a hcp (hexagonalclose-packed) structure, and a (0002) face that is primarily orientedparallel with respect to the surface of the nonmagnetic substrate. Inthe perpendicular magnetic recording medium, even when the recordingdensity is increased, effects of demagnetization at boundary regionsbetween recording bits are small, and clear boundaries of the recordingbits are formed, to the improve the noise property or SNR(Signal-to-Noise Ratio). Further, in the perpendicular magneticrecording medium, a decrease in a volume of the recording bits due tothe increase in the recording density is small, and the thermalstability can be improved. For this reason, various structures have beenproposed for the perpendicular magnetic recording medium.

A magnetic layer having a granular structure is used for theperpendicular magnetic layer. The magnetic layer having the granularstructure includes a nonmagnetic nonmetallic material at grain boundaryparts of magnetic grains. Hence, the nonmagnetic nonmetallic materialphysically isolates the magnetic grains, to reduce magnetic interactionbetween the magnetic grains, and reduce formation of a zigzag magneticdomain wall at a transition region of the recording bit. As a result, itis possible to improve the noise property.

Examples of the nonmagnetic nonmetallic material include oxides,nitrides, carbides, borides, or the like, as proposed in JapaneseLaid-Open Patent Publication No. 2007-257679, for example.

However, cobalt or the like easily precipitates into the magnetic layerhaving the granular structure, to deteriorate the corrosion resistanceof the magnetic recording medium.

For this reason, a magnetic recording medium proposed in JapaneseLaid-Open Patent Publication No. 2006-277950, for example, is providedwith two magnetic layers, and one of the two magnetic layers arrangedcloser to a protection layer has a non-granular structure.

However, when the magnetic layer having the non-granular structure isprovided, the noise property of the magnetic recording mediumdeteriorates.

SUMMARY OF THE INVENTION

Embodiments of the present invention can provide a magnetic recordingmedium and a magnetic storage apparatus, which can obtain superior noiseproperty and corrosion resistance.

According to one aspect of embodiments of the present invention, amagnetic recording medium includes a nonmagnetic substrate, a softmagnetic underlayer, an orientation control layer, a perpendicularmagnetic layer, and a protection layer that are arranged in this order,wherein the perpendicular magnetic layer includes a first magnetic layerand a second magnetic layer that are arranged in this order on theorientation control layer, wherein the first magnetic layer has agranular structure including an oxide at grain boundary parts ofmagnetic grains, and wherein the second magnetic layer is closest to theprotection layer among layers within the perpendicular magnetic layer,and includes magnetic grains made of a CoCrPt alloy, and a nitride ofcarbon or a hydride of carbon.

According to another aspect of the embodiments of the present invention,a magnetic storage apparatus includes the magnetic recording mediumreferred above; and a magnetic head configured to write information toand read information from the magnetic recording medium.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view illustrating an example of a structureof a magnetic recording medium in one embodiment of the presentinvention;

FIG. 2 is cross sectional view illustrating an example of a structure ofa perpendicular magnetic layer illustrated in FIG. 1;

FIG. 3 is a perspective view illustrating an example of a magneticstorage apparatus in one embodiment of the present invention; and

FIG. 4 is a table illustrating evaluation results of noise property andcorrosion resistance for exemplary implementations and comparisonexamples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments and exemplary implementations of a magnetic recording mediumand a magnetic storage apparatus according to the present invention willbe described, by referring to the drawings. In each of the embodimentsand exemplary implementations, the configuration, arrangements orpositions, materials, and amounts (at % or mol %) of elements used inthe magnetic recording medium or the magnetic storage apparatus may beappropriately modified, unless indicated otherwise.

FIG. 1 is a cross sectional view illustrating an example of a structureof the magnetic recording medium in one embodiment of the presentinvention.

A magnetic recording medium 10 illustrated in FIG. 1 includes anonmagnetic substrate 1, a soft magnetic underlayer 2, an orientationcontrol layer 3, a perpendicular magnetic layer 4, a protection layer 5,and a lubricant layer 6 that are arranged in this order.

The perpendicular magnetic layer 4 has a hcp structure, and a (0002)face that is primarily oriented parallel with respect to a surface ofthe nonmagnetic substrate 1. For this reason, an axis of easymagnetization of the perpendicular magnetic layer 4 is primarilyoriented perpendicularly to the surface of the nonmagnetic substrate 1.

The perpendicular magnetic layer 4 includes a first magnetic layer 4 a,and a second magnetic layer 4 b. The first magnetic layer 4 a isarranged on a side closer to the orientation control layer 3 than thesecond magnetic layer 4 b. In addition, the perpendicular magnetic layer4 includes arbitrary magnetic or nonmagnetic layers 7 a, 7 b, 7 c, 7 d,and 7 e, in addition to the first magnetic layer 4 a and the secondmagnetic layer 4 b. In the perpendicular magnetic layer 4, magnetic ornonmagnetic grains 41 form a columnar crystal that is continuous fromlower to upper layers, as illustrated in FIG. 2.

In the first magnetic layer 4 a and the second magnetic layer 4 b, thereference numeral “41” denotes a magnetic grain. In a case in which thelayers 7 a, 7 b, 7 c, 7 d, and 7 e are magnetic layers, the referencenumeral “41” denotes a magnetic grain. On the other hand, in a case inwhich the layers 7 a, 7 b, 7 c, 7 d, and 7 e are nonmagnetic layers, thereference numeral “41” denotes a nonmagnetic grain.

The first magnetic layer 4 a has a granular structure, including anoxide in grain boundary parts 42 of the magnetic grains 41. For thisreason, the magnetic grains 41 in the first magnetic layer 4 a areeasily isolated and refined, to improve the noise property of themagnetic recording medium 10.

In a case in which the first magnetic layer 4 a is formed by sputtering,the oxide has a highest reactivity among nonmagnetic nonmetallicmaterials forming the grain boundary parts 42. For this reason, when theoxide is used as the nonmagnetic nonmetallic material, it is possible toeasily form the first magnetic layer 4 a.

In addition, the second magnetic layer 4 b is a magnetic layer closestto the protection layer 5 within the perpendicular magnetic layer 4. Thesecond magnetic layer 4 b preferably has a granular structure includinga nitride of carbon (C) or a hydride of carbon (C), at the grainboundary parts 42 of the magnetic grains 41 made of a CoCrPt alloy. Forthis reason, similarly as in the case of the first magnetic layer 4 a,the magnetic grains 41 made of the CoCrPt alloy, in the second magneticlayer 4 b, are easily isolated and refined, to improve the noiseproperty of the magnetic recording medium 10.

The nitride of carbon or the hydride of carbon is stable compared to theoxide, and is uneasily oxidized. Further, the nitride of carbon or thehydride of carbon can prevent diffusion of the oxide from other layers.For this reason, it is possible to improve the corrosion resistance ofthe magnetic recording medium 10.

The second magnetic layer 4 b does not need to have the granularstructure, and need only include the magnetic grains made of the CoCrPtalloy, and the nitride of carbon or the hydride of carbon. Hence, themagnetic grains made of the CoCrPt alloy are isolated and refined, toimprove the noise property of the magnetic recording medium 10.

For example, the second magnetic layer 4 b may include the nitride ofcarbon or the hydride of carbon precipitated into a periphery of themagnetic grains 41. Alternatively, the nitride of carbon or the hydrideof carbon may precipitate into the magnetic grains 41.

A molar ratio of the oxide included in the first magnetic layer 4 a andforming the grain boundary parts 42, with respect to a magnetic materialforming the magnetic grains 41, is preferably 3% or higher and 18% orlower, and more preferably 6% or higher and 13% or lower. In a case inwhich the molar ratio of the oxide included in the first magnetic layer4 a and forming the grain boundary parts 42, with respect to themagnetic material forming the magnetic grains 41, is 3% or higher and18% or lower, the noise property of the magnetic recording medium 10improves.

The oxide forming the grain boundary parts 42 included in the firstmagnetic layer 4 a is preferably an oxide of an element selected from agroup consisting of silicon (Si), chromium (Cr), titanium (Ti), tantalum(Ta), aluminum (Al), yttrium (Y), boron (B), magnesium (Mg), tungsten(W), and cobalt (Co).

Examples of the magnetic material forming the magnetic grains 41included in the first magnetic layer 4 a include CoCrPt—SiO₂,CoCrPtNb—Cr₂O₃, CoCrPt—Ta₂O₅, CoCrPt—Cr₂O—TiO₂, COCrPt—Cr₂O₃—SiO₂,COCrPt—Cr₂O₃—SiO₂—TiO₂, CoCrPtMo—TiO₂, CoCrPtW—TiO₂, CoCrPtB—Al₂O₃,CoCrPtTaNd—MgO, CoCrPtBCu—Y₂O₃, CoCrPtRu—SiO₂, or the like, for example.

The second magnetic layer 4 b preferably includes no oxide. In thiscase, the corrosion resistance of the magnetic recording medium 10improves.

The second magnetic layer 4 b may be formed by forming a magnetic layerthat includes magnetic grains made of the CoCrPt alloy, and carbon, bysputtering, for example, and thereafter subjecting the magnetic layer toa nitriding treatment or a hydriding treatment, so that at least a partof the carbon included in the magnetic layer is nitrided or hydrided.

A known method may be used for a method of subjecting the magnetic layerto the nitriding treatment. From a viewpoint of reducing damage to themagnetic layer, the method of subjecting the magnetic layer to thenitriding treatment preferably exposes the magnetic layer to reactivenitrogen plasma.

A known method may be used for a method of subjecting the magnetic layerto the hydriding treatment. From a viewpoint of reducing damage to themagnetic layer, the method of subjecting the magnetic layer to thehydriding preferably exposes the magnetic layer to reactive hydrogenplasma.

In addition, the second magnetic layer 4 b may be formed by forming amagnetic layer that includes magnetic grains made of the CoCrPt alloy,and carbon, by reactive sputtering, so that nitrogen or hydrogen isintroduced into a sputtering gas.

Examples of CoCrPt alloy materials forming the magnetic grains includedin the second magnetic layer 4 b include CoCrPt alloys, CoCrPtB alloys,CoCrPtTa alloys, CoCrPtTi alloys, CoCrPtZr alloys, CoCrPtAl alloys,CoCrPtSi alloys, or the like, for example.

The CoCrPt alloy forming the magnetic grains preferably includes noboron, for the following reasons. That is, in a case in which a methodof manufacturing the magnetic recording medium 10 includes a heattreatment and the CoCrPt alloy forming the magnetic grains includeboron, the boron within the magnetic grains made of the CoCrPt alloythermally diffuses to change the composition. In this case, the grainboundary parts of the magnetic grains easily become unclear, and anelectromagnetic conversion property of the magnetic recording medium 10may deteriorate.

Examples of the material forming the second magnetic layer 4 b includeCoCrPt—CNx, CoCrPtB—CNx, CoCrPtTa—CNx, CoCrPtTi—CNx, CoCrPtZr—CNx,CoCrPtAl—CNx, CoCrPtSi—CNx, CoCrPt—CHx, CoCrPtB—CHx, CoCrPtTa—CHx,CoCrPtTi—CHx, CoCrPtZr—CHx, CoCrPtAl—CHx, CoCrPtSi—CHx, or the like, forexample, where “x” is an arbitrary number, and each of “—CNx” and “—CHx”may be any one of crystalline structure, amorphous structure, and amixture of crystalline and amorphous structures.

A content of the nitride of carbon or the hydride of carbon within thesecond magnetic layer 4 b is preferably in a range of 1 mol % to 50 mol%, and is more preferably in a range of 10 mol % to 40 mol %. In a casein which the content of the nitride of carbon or the hydride of carbonwithin the second magnetic layer 4 b is in the range of 1 mol % to 50mol %, the noise property of the magnetic recording medium 10 improves.

In a case in which the grain boundary parts of the magnetic layer havingthe granular structure is formed by an oxide of silicon, chromium,titanium, or the like, a content of the oxide within the magnetic layerin most cases is approximately 10 mol %. However, because the nitride ofcarbon or the hydride of carbon included within the second magneticlayer 4 b is formed by an element having a small atomic weight or mass,the content [mol %] of the oxide within the magnetic layer tends tobecome large.

The magnetic grains made of the CoCrPt alloy preferably includes thenitride of carbon or the hydride of carbon in a range of 1 mol % to 8mol %. In this case, the corrosion resistance of the magnetic grainsmade of the CoCrPt alloy improves, to improve the corrosion resistanceof the magnetic recording medium 10.

The perpendicular magnetic layer 4 includes the arbitrary magnetic ornonmagnetic layers 7 a, 7 b, 7 c, 7 d, and 7 e. However, the layers 7 aand 7 c are preferably magnetic layers, and the layers 7 b, 7 d, and 7 eare preferably nonmagnetic layers.

The number of arbitrary magnetic or nonmagnetic layers is not limited tofive, and the number may be increased or decreased if necessary.

The arbitrary magnetic layer preferably has the granular structureincluding the oxide in the grain boundary parts 42 of the magneticgrains 41, similarly to the first magnetic layer 4 a.

The material forming the arbitrary magnetic layer is the same as thematerial forming the first magnetic layer 4 a.

The arbitrary nonmagnetic layer is provided between the magnetic layersto control an exchange coupling between the magnetic layers.

The material forming the arbitrary nonmagnetic layer preferably has thehcp structure.

Examples of the material forming the arbitrary nonmagnetic layer includeRu, Ru alloys, RuCo alloys, CoCr alloys, and CoCrX alloys, for example,where “X” is one or more elements selected from a group consisting ofPt, Ta, Zr, Re, Ru, Cu, Nb, Ni, Mn, Ge, Si, O, N, W, Mo, Ti, V, Zr, andB.

In addition, the arbitrary nonmagnetic layer may have the granularstructure.

A thickness of the arbitrary nonmagnetic layer needs to be in a rangesuch that ferromagnetic coupling of the first magnetic layer 4 a, thesecond magnetic layer 4 b, and the arbitrary magnetic layers will not becut off completely.

Next, other structures of the magnetic recording medium 10 will bedescribed.

A metal substrate formed by a metal material such as aluminum, aluminumalloys, or the like, may be used for the nonmagnetic substrate 1.Alternatively a nonmetallic substrate formed by a nonmetallic materialsuch as glass, ceramics, silicon, silicon carbide, carbon, or the like,may be used for the nonmagnetic substrate 1.

Each of the metal substrate and the nonmetallic substrate may have a NiPlayer or a NiP alloy layer formed on a surface thereof by plating orsputtering.

The soft magnetic underlayer 2 is provided to increase a perpendicularcomponent of magnetic flux generated from a magnetic head with respectto the nonmagnetic substrate, and to more strongly pin the axis of easymagnetization of the perpendicular magnetic layer 4 in a directionperpendicular to the nonmagnetic substrate 1. In a case in which asingle-pole head for perpendicular recording is used as the magnetichead that records information on the magnetic recording medium 10, theaction of the soft magnetic underlayer 2 becomes more notable.

The material forming the soft magnetic underlayer 2 is not limited to aparticular material. Examples of the material forming the soft magneticunderlayer 2 include soft magnetic materials including Fe,

Ni, and Co.

Examples of the soft magnetic material include CoFe alloys, FeCo alloys,FeNi alloys, FeAl alloys, FeCr alloys, FeTa alloys, FeMg alloys, FeZralloys, FeC alloys, FeN alloys, FeSi alloys, FeP alloys, FeNb alloys,FeHf alloys, FeB alloys, or the like, for example. The CoFe alloysinclude CoFeTaZr, CoFeZrNb, or the like. The FeCo alloys include FeCo,FeCoV, or the like. The FeNi alloys include FeNi, FeNiMo, FeNiCr,FeNiSi, or the like. The FeAl alloys, include FeAl, FeAlSi, FAlSiCr,FeAlSiTiRu, FeAlO, or the like. The FeCr alloys include FeCr, FeCrTi,FeCrCu, or the like. The FeTa alloys include FeTa, FeTaC, FeTaN, or thelike. The FeMg alloys include FeMgO, or the like. The FeZr alloysinclude FeZrN, or the like.

The soft magnetic underlayer 2 is preferably formed by two soft magneticlayers sandwiching a Ru layer. The Ru layer preferably has a thicknessadjusted to a range of 0.4 nm to 1.0 nm, or a range of 1.6 nm to 2.6 nm.In this case, the two soft magnetic layers form an AFC(Anti-Ferromagnetic Coupling) structure, to thereby reduce the so-calledspike noise.

An adhesion layer (or bonding layer) is preferably provided between thenonmagnetic substrate 1 and the soft magnetic underlayer 2. In thiscase, the corrosion resistance of the magnetic recording medium 10 isimproved.

Examples of the material forming the adhesion layer include Cr, Cralloys, Ti, Ti alloys, or the like, for example. The adhesion layerpreferably has a thickness of 30 Å or greater.

The orientation control layer 3 controls the orientation of theperpendicular magnetic layer 4. In other words, the orientation controllayer 3 is provided to primarily orient the (0002) face of theperpendicular magnetic layer 4 having the hcp structure, parallel withrespect to the surface of the nonmagnetic substrate 1. Hence, themagnetic grains 41 of the perpendicular magnetic layer 4 are refined, toimprove the noise property of the magnetic recording medium 10.

The material forming the orientation control layer 3 preferably has thehcp structure, a fcc (face-centered cubic) structure, or an amorphousstructure.

Examples of the material forming the orientation control layer 3 includeRu alloys, Ni alloys, Co alloys, Pt alloys, Cu alloys, or the like, forexample.

The orientation control layer 3 may be formed by a plurality oforientation control layers. In this case, the orientation control layer3 arranged on the soft magnetic underlayer 2 preferably has amulti-layer structure including layers of Ni alloy and Ru alloy, amulti-layer structure including layers of Co alloy and Ru alloy, or amulti-layer structure including layers of Pt alloy and Ru alloy, forexample.

The protection layer 5 is provided to prevent corrosion of theperpendicular magnetic layer 4, and to prevent damage to the surface ofthe magnetic recording medium 10 when the magnetic head contacts themagnetic recording medium 10.

Known materials may be used as the material forming the protection layer5. Examples of the material forming the protection layer 5 include hardcarbon, or the like, for example.

The protection layer 5 preferably has a thickness of 1 nm to 10 nm. Inthis case, a distance between the magnetic head and the magneticrecording medium 10 can be reduced, so that it is possible to providethe magnetic recording medium 10 suited for the high-density recording.

Examples of the material forming the lubricant layer include lubricantssuch as perfluoropolyether, fluorinated alcohol, fluorinated carboxylicacid, or the like, for example.

FIG. 3 is a perspective view illustrating an example of a magneticstorage apparatus in one embodiment of the present invention.

The magnetic storage apparatus illustrated in FIG. 3 includes at leastone magnetic recording medium 10, a driving mechanism 11 that drives themagnetic recording medium 10 in a rotating direction, at least onemagnetic head 12, a head moving mechanism 13 that moves the magnetichead 12 relative to the magnetic recording medium 10, and a signalprocessor 14 that are accommodated within a casing 100. The magneticrecording medium 10 has the structure illustrated in FIG. 1. Themagnetic head 12 records information on and reproduces information fromthe magnetic recording medium 10.

The signal processor 14 processes input data received from an outsideinto a recording signal that is supplied to the magnetic head 12. Inaddition, the signal processor 14 processes a reproduced signal outputfrom the magnetic head 12 into data output to the outside.

The magnetic head 12 may be formed by a magnetic head suited for thehigh-density recording, and including as a reproducing element a GMR(Giant Magneto-Resistive) element that utilizes the GMR effect.

Next, exemplary implementations according to the present invention,together with comparison examples, will be described. However, thepresent invention is not limited to these exemplary implementations, andvarious variations, modifications, and substitutions may be made withoutdeparting from the scope of the present invention.

(Exemplary Implementation EI1)

The magnetic recording medium is manufactured by the following method.

First, a cleaned nonmagnetic substrate (manufactured by HOYACorporation) made of glass and having an outer diameter of 2.5 inches isaccommodated within a deposition chamber of a DC magnetron sputteringapparatus C-3040 (manufactured by CANON ANELVA CORPORATION), and thedeposition chamber is evacuated to an ultimate pressure of 1×10⁻⁵ Pa.

Next, a Cr50Ti {Ti-content of 50 at %, remainder Cr} target is used toform an adhesion layer to a thickness of 10 nm on the nonmagneticsubstrate.

Next, a Co20Fe5Zr5Ta {Fe-content of 20 at %, Zr-content of 5 at %,Ta-content of 5 at %, and remainder Co} target is used to form a softmagnetic layer to a thickness of 25 nm on the adhesion layer by settinga temperature of the nonmagnetic substrate to 100° C.

Next, a Ru target is used to form a Ru layer to a thickness of 0.7 nm onthe soft magnetic layer.

Next, the Co20Fe5Zr5Ta target is used to form a soft magnetic underlayerto a thickness of 25 nm on the Ru layer by setting the temperature ofthe nonmagnetic substrate to 100° C.

Next, a Ni6W {W-content of 6 at %, and remainder Ni} target and a Rutarget are used to respectively form a Ni-6W layer having a thickness of5 nm and a Ru layer having a thickness of 20 nm, in this order on thesoft magnetic underlayer, to form an orientation control layer.

Next, a 91(Co15Cr18Pt)-6(SiO₂)-3 (TiO₂) {alloy-content of 91 mol % ofalloy including Cr-content of 15 at %, Pt-content of 18 at %, andremainder Co, SiO₂-content of 6 mol %, and TiO₂-content of 3 mol %}target is used to form a magnetic layer having a granular structure to athickness of 9 nm on the orientation control layer, with a sputteringpressure set to 2 Pa.

Next, a 88(Co30Cr)-12(TiO2) {alloy-content of 88 mol % of alloyincluding Cr-content of 30 at %, and remainder Co, and TiO2-content of12 mol %} target is used to form a nonmagnetic layer having a granularstructure to a thickness of 0.3 nm on the magnetic layer.

Next, a 92(Co11Cr18Pt)-5(SiO₂)-3(TiO₂) {alloy-content of 92 mol % ofalloy including Cr-content of 11 at %, Pt-content of 18 at %, andremainder Co, SiO₂-content of 5 mol %, and TiO₂-content of 3 mol %}target is used to form a first magnetic layer having a granularstructure to a thickness of 6 nm on the nonmagnetic layer, with thesputtering pressure set to 2 Pa.

Next, a Ru target is used to form a nonmagnetic layer having anon-granular structure to a thickness of 0.3 nm on the first magneticlayer.

Next, a 70(Co11Cr18Pt)-30C {alloy-content of 70 mol % of alloy includingCr-content of 11 at %, Pt-content of 18 at %, and remainder Co, andC-content of 30 mol %} target is used to form a magnetic layer having agranular structure to a thickness of 10 nm on the nonmagnetic layerprovided on the first magnetic layer, with the sputtering pressure setto 0.6 Pa.

Next, the magnetic layer having the granular structure and the thicknessof 10 nm is exposed to reactive nitrogen plasma for 20 seconds tosubject this magnetic layer to a nitriding treatment, to form a secondmagnetic layer having the granular structure and made of70(Co11Cr18Pt)-30(CN_(2.5)) {alloy-content of 70 mol % of alloyincluding Cr-content of 11 at %, Pt-content of 18 at %, and remainderCo, and CN_(2.5)-content of 30 mol %}. The reactive nitrogen plasma isgenerated by applying a RF (Radio Frequency) power of 500 W to a mixturegas in which nitrogen gas content is 5 vol % and argon gas content is 95vol %. An amount of nitridization of C is measured using a SIMS(Secondary Ion Mass Spectrometer). In addition, a structure of thenitride of C is analyzed using a TEM (Transmission Electron Microscope),and found to be an amorphous structure.

Next, ion beam epitaxy is used to form a protection layer to a thicknessof 2 nm on the second magnetic layer.

Next, dipping is used to form a lubricant layer made ofperfluoropolyether on the protection layer, to manufacture the magneticrecording medium.

(Exemplary Implementation IE2)

When forming the second magnetic layer, the magnetic layer having thegranular structure and the thickness of 10 nm is exposed to reactivehydrogen plasma for 10 seconds to subject this magnetic layer to ahydriding treatment, to form a second magnetic layer having a granularstructure and made of 70(Co11Cr18Pt)-30(CH_(3.5)) {alloy-content of 70mol % of alloy including Cr-content of 11 at %, Pt-content of 18 at %,and remainder Co, and CH_(3.5)-content of 30 mol %}. Otherwise, themagnetic recording medium is manufactured similarly to the exemplaryimplementation IE1. The reactive hydrogen plasma is generated byapplying a RF power of 500 W to a mixture gas in which hydrogen gascontent is 8 vol % and argon gas content is 92 vol %. An amount ofhydrization of C is measured using the SIMS. In addition, a structure ofthe hydride of C is analyzed using the TEM, and found to be an amorphousstructure.

(Exemplary Implementation EI3)

When forming the second magnetic layer, a 70(Co10Cr20Pt14B)-30C targetis used to form a magnetic layer having a granular structure and made of70(Co10Cr20Pt14B)-30(CN_(2.5)) {alloy-content of 70 mol % of alloyincluding Cr-content of 10 at %, Pt-content of 20 at %, B-content of 14at %, and remainder Co, and CN_(2.5)-content of 30 mol %}. Otherwise,the magnetic recording medium is manufactured similarly to the exemplaryimplementation IE1. A structure of the nitride of C is analyzed usingthe TEM, and found to be an amorphous structure.

(Exemplary Implementation EI4)

When forming the second magnetic layer, a 70(Co10Cr20Pt14B)-30C targetis used to form a magnetic layer having a granular structure and made of70(Co10Cr20Pt14B)-30(CH_(3.5)) {alloy-content of 70 mol % of alloyincluding Cr-content of 10 at %, Pt-content of 20 at %, B-content of 14at %, and remainder Co, and CH_(3.5)-content of 30 mol %}. Otherwise,the magnetic recording medium is manufactured similarly to the exemplaryimplementation IE2. A structure of the nitride of C is analyzed usingthe TEM, and found to be an amorphous structure.

(Exemplary Implementation EI5)

When forming the second magnetic layer, a70[95(Co11Cr14Pt)-5(CN_(2.1))]-30C {alloy-content of 70 mol % of alloythat includes 95 mol % of a first alloy including Cr-content of 11 at %,Pt-content of 14 at %, and remainder Co, and 5 mol % of a second alloyincluding CN_(2.1), and a C-content of 30 mol %} target is used to forma magnetic layer having a granular structure and made of70[95(Co11Cr14Pt)-5(CN_(2.1))]-30(CN_(2.5)) {alloy-content of 70 mol %of alloy that includes 95 mol % of a first alloy including Cr-content of11 at %, Pt-content of 14 at %, and remainder Co, and 5 mol % of asecond alloy including CN_(2.1), and a CN_(2.5)-content of 30 mol %}.Otherwise, the magnetic recording medium is manufactured similarly tothe exemplary implementation IE1. A structure of the nitride of C isanalyzed using the TEM, and found to be an amorphous structure.

(Exemplary Implementation IE6)

When forming the second magnetic layer, a70[95(Co11Cr14Pt)-5(CH_(3.1))]-30C {alloy-content of 70 mol % of alloythat includes 95 mol % of a first alloy including Cr-content of 11 at %,Pt-content of 14 at %, and remainder Co, and 5 mol % of a second alloyincluding CH_(3.1), and a C-content of 30 mol %} target is used to forma magnetic layer having a granular structure and made of70[95(Co11Cr14Pt)-5(CH_(3.1))]-30(CH_(3.5)) {alloy-content of 70 mol %of alloy that includes 95 mol % of a first alloy including Cr-content of11 at %, Pt-content of 14 at %, and remainder Co, and 5 mol % of asecond alloy including CH_(3.1), and a CH_(3.5)-content of 30 mol %}.Otherwise, the magnetic recording medium is manufactured similarly tothe exemplary implementation IE2. A structure of the nitride of C isanalyzed using the TEM, and found to be an amorphous structure.

Comparison Example CE1

When forming the second magnetic layer, a Co10Cr20Pt14B target is used,and no nitriding treatment is performed, to form a magnetic layer havinga non-granular structure. Otherwise, the magnetic recording medium ismanufactured similarly to the exemplary implementation IE1.

Comparison Example CE2

When forming the second magnetic layer, a 92(Co11Cr18Pt)-5(SiO₂)-3(TiO₂)target is used, and no nitriding treatment is performed, to form amagnetic layer having a granular structure. Otherwise, the magneticrecording medium is manufactured similarly to the exemplaryimplementation IE1.

Comparison Example CE3

When forming the second magnetic layer, no nitriding treatment isperformed, to form a magnetic layer having a granular structure.Otherwise, the magnetic recording medium is manufactured similarly tothe exemplary implementation IE1.

Next, the noise property and the corrosion resistance of the magneticrecording media according to the exemplary implementations EI1 to EI6and the comparison examples CE1 to CE3 are evaluated.

(Noise Property)

A read-write analyzer RWA1632 and a spin-stand S1701MP manufactured byGuzik Technical Enterprises are used to measure the SNR [dB] of themagnetic recording media, to evaluate the noise property of the magneticrecording media.

(Corrosion Resistance)

Each magnetic recording medium is left to stand for 96 hours in anenvironment of 90° C. and 90% RH. Thereafter, an optical surfaceanalyzer is used to count the number of corrosion spots generated persurface, on the surface of each magnetic recording medium, to evaluatethe corrosion resistance. A detection accuracy of the corrosion spot isset to a diameter of 5 μm or greater.

FIG. 4 is a table illustrating evaluation results of noise property andcorrosion resistance for the exemplary implementations EI1 to EI6 andthe comparison examples CE1 to CE3.

It was confirmed from the table of FIG. 4 that the magnetic recordingmedia according to the exemplary implementations IE1 to IE6 havesuperior noise property and superior corrosion resistance.

On the other hand, it was confirmed from the table of FIG. 4 that themagnetic recording medium according to the comparison example CE1 has apoor noise property because the second magnetic layer does not includethe nitride of carbon nor the hydride of carbon.

It was confirmed from the table of FIG. 4 that the magnetic recordingmedium according to the comparison example CE2 has an extremely poorcorrosion resistance because the second magnetic layer does not includethe nitride of carbon nor the hydride of carbon, and includes an oxideinstead.

It was confirmed from the table of FIG. 4 that the magnetic recordingmedium according to the comparison example CE3 has a poor corrosionresistance because the second magnetic layer does not include thenitride of carbon nor the hydride of carbon, and includes carboninstead.

Hence, according to the embodiments an exemplary implementationsdescribed above, it is possible to provide a magnetic recording mediumand a magnetic storage apparatus, which can obtain superior noiseproperty and corrosion resistance.

Although the embodiments and the exemplary implementations are numberedwith, for example, “first,” “second,” “third,” etc., the ordinal numbersdo not imply priorities of the embodiments and the exemplaryimplementations.

Further, the present invention is not limited to these embodiments andexemplary implementations, but various variations and modifications maybe made without departing from the scope of the present invention.

What is claimed is:
 1. A magnetic recording medium comprising: anonmagnetic substrate, a soft magnetic underlayer, an orientationcontrol layer, a perpendicular magnetic layer, and a protection layerthat are arranged in this order, wherein the perpendicular magneticlayer includes a first magnetic layer and a second magnetic layer thatare arranged in this order on the orientation control layer, wherein thefirst magnetic layer has a granular structure including an oxide atgrain boundary parts of magnetic grains, and wherein the second magneticlayer is closest to the protection layer among layers within theperpendicular magnetic layer, and includes magnetic grains made of aCoCrPt alloy, and a nitride of carbon which precipitates into themagnetic grains.
 2. The magnetic recording medium as claimed in claim 1,wherein the second magnetic layer includes the nitride of carbon in arange of 1 mol % to 50 mol % at grain boundary parts of the magneticgrains made of the CoCrPt alloy.
 3. The magnetic recording medium asclaimed in claim 1, wherein the oxide is an oxide of an element selectedfrom a group consisting of silicon, chromium, titanium, tantalum,aluminum, yttrium, boron, magnesium, tungsten, and cobalt.
 4. Themagnetic recording medium as claimed in claim 1, wherein the magneticgrains made of the CoCrPt alloy includes no boron.
 5. The magneticrecording medium as claimed in claim 1, wherein the second magneticlayer includes no oxide.
 6. The magnetic recording medium as claimed inclaim 1, wherein the second magnetic layer has a granular structureincluding the nitride of carbon at grain boundary parts of the magneticgrains made of the CoCrPt alloy, and wherein the magnetic grains made ofthe CoCrPt alloy includes the nitride of carbon in a range of 1 mol % to8 mol %.
 7. A magnetic storage apparatus comprising: the magneticrecording medium according to claim 1; and a magnetic head configured towrite information to and read information from the magnetic recordingmedium.
 8. The magnetic storage apparatus as claimed in claim 7, whereinthe second magnetic layer of the magnetic recording medium includes thenitride of carbon in a range of 1 mol % to 50 mol % at grain boundaryparts of the magnetic grains made of the CoCrPt alloy.
 9. The magneticstorage apparatus as claimed in claim 7, wherein the oxide is an oxideof an element selected from a group consisting of silicon, chromium,titanium, tantalum, aluminum, yttrium, boron, magnesium, tungsten, andcobalt.
 10. The magnetic storage apparatus as claimed in claim 7,wherein the magnetic grains made of the CoCrPt alloy includes no boron.11. The magnetic storage apparatus as claimed in claim 7, wherein thesecond magnetic layer of the magnetic recording medium includes nooxide.
 12. The magnetic storage apparatus as claimed in claim 7, whereinthe second magnetic layer of the magnetic recording medium has agranular structure including the nitride of carbon at grain boundaryparts of the magnetic grains made of the CoCrPt alloy, and wherein themagnetic grains made of the CoCrPt alloy includes the nitride of carbonin a range of 1 mol % to 8 mol %.